Circuit protection device

ABSTRACT

A circuit protection device includes a conductive layer which is connected to first and second terminals. A spring is electrically connected to the first and second terminals. When an over-voltage or over-temperature condition occurs within a charging circuit, one or more heat generating resistive elements melts material associated with one or more of the ends of the spring thereby releasing the spring to create an open circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to the field of circuit protectiondevices. More particularly, the present invention relates to aprotection device that generates heat in an over-voltage orover-temperature situation which melts connections to a spring whichthen operates creating an open circuit thereby protecting a power sourceand related circuitry.

2. Discussion of Related Art

Over-voltage and over-temperature protection devices utilize thermallinks which can melt during an abnormal situation to form an opencircuit. These protection devices may be disposed between, for example,a charger and a plurality of rechargeable battery cells (e.g. Li ionbatteries). When a voltage that is larger than the threshold voltage isapplied to the sensing and trigger circuitry, current flows through heatgenerating members causing one of more thermal links to melt. Once thelinks are melted, an open circuit is created which prevents theover-voltage condition from damaging the battery cells. In another typeof protection device, thermal cut-off functionality is used to protectthe power source, e.g. battery cells. When the temperature of the cellsexceeds a particular threshold level, one or more thermal links meltcreating an open circuit thereby separating the charging device from thebattery cells. However, the thermal coupling between the cells where theover-temperature condition exists and the thermal links may not besufficient to ensure adequate response time, resulting in a thermalrun-away condition. Accordingly, there is a need to provide a protectiondevice configured to result in a sufficiently fast response to protectthe battery cells.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention are directed to aprotection device disposed between a charger and a one or more batterycells to be charged. In an exemplary embodiment, a protection deviceincludes an electrically conductive spring, a pair of low meltingmembers and one or more heat generating resistive elements disposed on asubstrate. The electrically conductive spring has a first end connectedto a first of the pair of low melting members and a second end connectedto a second of the pair of low melting members. The low melting membersmay be solder joints that melt from the heat generated by the resistiveelements. When at least one of the solder joints melts sufficiently inresponse to current generated from an over-voltage or over-temperaturecondition, the corresponding end of the spring snaps opening the circuitformed between the solder joints and the spring, thereby creating anopen circuit.

In another exemplary embodiment of the present invention a protectiondevice includes a substrate, a conducting layer, a resistive element, aconducting pad, a diffusion layer and a glass layer. The conductinglayer is disposed on the substrate and has at least a first and secondterminals. The resistive element is disposed at least partially on theconducting layer. The conducting pad is disposed over the resistiveelement. The diffusion layer is disposed over the conducting pad. Theglass layer is disposed over the diffusion layer wherein when anabnormal circuit condition occurs heat is generated by the resistiveelement which causes a portion of the diffusion layer to diffuse intothe glass layer to create an open circuit between the first and secondterminals.

In another exemplary embodiment of the present invention a protectiondevice includes a substrate; a conducting layer disposed on thesubstrate where the conducting layer has at least a first and secondterminals; a resistive element is disposed at least partially on theconducting layer; a conducting pad is disposed over the resistiveelement; a thermal link layer is disposed over the conducting pad; and ahot melt adhesive (HMA) cover layer is disposed over the thermal linklayer wherein when an abnormal circuit condition occurs heat isgenerated by the resistive element which causes a portion of the HMAlayer to absorb the thermal link layer to create an open circuit betweenthe first and second terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1K illustrate layers of a protection device in accordance withan embodiment of the present disclosure.

FIG. 2A-2I illustrate layers of a protection device in accordance withan alternative embodiment of the present disclosure.

FIGS. 3A-3H illustrate layers of a protection device in accordance withan alternative embodiment of the present disclosure.

FIGS. 4A-4G illustrate layers of a protection device in accordance withan alternative embodiment of the present disclosure.

FIGS. 5A-5G illustrate layers of a protection device in accordance withan alternative embodiment of the present disclosure.

FIG. 6 illustrates a top plan view of an exemplary cover of a protectiondevice in accordance with an embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention, however, may be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, like numbers refer to like elements throughout.

In the following description and/or claims, the terms “on,” “overlying,”“disposed on” and “over” may be used in the following description andclaims. “On,” “overlying,” “disposed on” and “over” may be used toindicate that two or more elements are in direct physical contact witheach other. However, “on,”, “overlying,” “disposed on,” and over, mayalso mean that two or more elements are not in direct contact with eachother. For example, “over” may mean that one element is above anotherelement but not contact each other and may have another element orelements in between the two elements. Furthermore, the term “and/or” maymean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean“one”, it may mean “some, but not all”, it may mean “neither”, and/or itmay mean “both”, although the scope of claimed subject matter is notlimited in this respect.

FIG. 1A-1K illustrate a circuit protection device 10 in accordance withthe present disclosure. A first layer 12 is defined by metallizedconducting paths 22, 24 and first terminal 20 ₁, second terminal 20 ₂,third terminal 20 ₃ and fourth terminal 20 ₄ disposed on substrate 15.Metallized conducting path 22 includes pad 21. First terminal 20 ₁ andsecond terminal 20 ₂ are used to connect the protection device 10between a source of charge and a device to be protected, for example, aplurality of battery cells. Third terminal 20 ₃ is connected toconducting path 24 and provides an electrical connection to a controlcircuit (e.g. sensing circuit and transistor) which provides anover-voltage or over-temperature signal to protection device 10.

FIG. 1B illustrates a first resistive element 32 and second resistiveelement 34 disposed on and between conducting paths 22 and 24.Alternatively, a single resistive element which extends between thepaths may be used or just one resistive element may be employed tocreate enough heat to melt at least one solder joint as described below.Alternative geometries for the resistive elements 32 and 34 may bemodified to provide robustness to the voltage applied thereto. Thesegeometries are intended to provide heat to the solder pads 46, 47 for alonger period of time, if necessary, as described in more detail below.

FIG. 1C illustrates a dielectric layer 35 disposed on substrate 15 whichcovers resistive elements 32 and 34. An opening 36 is formed throughdielectric layer 35 to provide a connection means to conducting path 22.Dielectric layer 35 may be, for example, a glass having a desiredthermal conductivity to allow heat generated by the resistors 32, 34 topass therethrough.

FIG. 1D illustrates a first conducting pad 42 disposed on dielectriclayer 35 above first resistive element 32 and a second conducting pad 44disposed on dielectric layer 35 above second resistive element 34. Firstconducting pad 42 forms a connection with first terminal 20 ₁ and secondconducting pad 44 forms a connection with second terminal 20 ₂.

FIG. 1E illustrates a dielectric layer 45 for example, glass, disposedpartially over conducting pads 42, 44 and opening 36, resulting inexposed portions of the underlying conducting pads which become solderjoint pads 46, 47 and 48. Low temperature melt solder is disposed onsolder pads 46, 47 and 48. Pad 48 is used to conduct current from aspring (shown in FIG. 1F) to a control circuit via terminal 20 ₃ duringan abnormal circuit condition as discussed below.

FIG. 1F illustrates a generally “U” shaped flat spring 50 having a pairof sides 50 ₁, 50 ₂ extending from an apex portion 51. The respectiveends of the sides 50 ₁, 50 ₂ are connected to solder pads 46 and 47using solder 46′, 47′ and the apex 51 is soldered to solder pad 48.Spring 50 may be made from, for example, high carbon steel plated withsilver, a shape memory alloy material, or similar conducting materialand may, of course, have alternative configurations. A plastic cover (asshown in FIG. 6) is disposed over the circuit protection device 10 andglued about ledge 59 around the perimeter of substrate 12.

FIG. 1G is a schematic view of protective device 10 including resistiveelements 32, 34, low melt solder material 46′, 47′ and first terminal 20₁, second terminal 20 ₂ and third terminal 20 ₃. The location of thesolder pads 46 and 47 (and consequently resistive elements 32 and 34)may be located more toward the apex portion 51 of spring 50 along springsides 50 ₁ and/or 50 ₂. This may be used to increase the reliabilitywhen the soldered connections 46′ and 47′ melt causing spring 50 tocreate an open circuit. In addition, the geometry of the solder pads 46,47 (and 48) may be modified to increase the surface area if more solderis needed to retain spring 50 in position. Furthermore, more than onesolder pad 46, 47 may be associated with each spring side 50 ₁, 50 ₂. Inparticular, spring side 501 may include pad 46 as well as another paddisposed between pad 46 and pad 48 at the apex of spring 50. Similarly,spring side 502 may include pad 47 and another pad disposed between pad47 and 48 at the apex of spring 50. Consequently, additional solderedconnections would also be employed with each additional pad and theassociated resistive element (e.g. resistive element 32 for pad 46) oran additional resistive element would be utilized to melt the solderedconnection.

FIG. 1H is a plan view of the various layers of the protection device 10shown in shadow disposed on substrate 12 and the associated current flowin a normal conducting situation. During normal operation, current flows(as indicated by the solid arrows) from terminal ₂ 0 ₁ to terminal ₂ 0 ₂the device to be protected.

As shown in FIG. 1I, when an over-voltage or over-temperature situationis detected, a control circuit (not shown) connected to terminal 20 ₃closes the circuit and draws current from the spring 50 via conductingpath 22. This current (indicated by the dashed arrows) flows throughresistors 32 and 34 which produces heat and melts one or more of thesoldered connections 46′ and/or 47′ via conducting pads 42 and 44. Thesolder material used may include flux which prevents oxidation of thesurface of the solder when it melts, which otherwise might result insmearing or dragging of the solder during spring operation. The meltingof one of more of the solder joints snaps at least one of the sides 50₁, and/or 50 ₂ of spring 50 closed. This creates an open circuit betweenthe source of charge and the device to be protected.

FIG. 1J illustrates the spring 50 after the abnormal circuit conditionhas occurred based on the melting of both the solders 46′, 47′ from theheating of resistive elements 32 and 34. Of course, if only a singleresistor configuration is used, wherein the resistor extends undersolder pads 46 and 47, the protection device operates in a similarfashion. In this manner, protection device 10 utilizes a spring disposedwithin a plurality of layers that produces an open circuit when anundesirable electrical or thermal condition occurs within a battery orcharging circuit. In an alternative embodiment, only one of the springsides (e.g. 50 ₁) may be displaced and the other spring side (e.g. 50 ₂)is stationary of fixed in position. The same solder pads and soldermaterial may be used to retain the stationary spring side in place sincea resistive element may not be located beneath the solder pad, therebyavoiding the heating of the solder material.

Alternatively (as shown in FIG. 1K), protection device 10 may include amajor current carrying shunt 80 connected between the ends of spring 50.Under normal charge and discharge conditions, shunt 80 carries themajority of the current allowing the use of spring alloys with higherelectrical resistance but improved spring properties. When anover-voltage or over-temperature condition occurs, the resistiveelements 32 and 34 heat forcing the spring to lose contact with at leastone of the solder pads 46 and 47, thereby compressing the shunt toproduce an open circuit.

FIG. 2A-2J illustrates a circuit protection device 10′ in accordancewith the present disclosure. A first layer 12 is defined by metallizedconducting paths 22, 24 and first terminal 20 ₁, second terminal 20 ₂,third terminal 20 ₃ and fourth terminal 20 ₄ disposed on substrate 15.Metallized conducting path 22 includes pad 21. First terminal 20 ₁ andsecond terminal 20 ₂ are used to connect the protection device 10between a source of charge and a device to be protected, for example,one or more battery cells. Third terminal 20 ₃ is connected toconducting path 24 and provides an electrical connection to a controlcircuit (e.g. transistor) which provides an over-voltage signal toprotection device 10.

FIG. 2B illustrates a first resistive element 32 and second resistiveelement 34 disposed on and between conducting paths 22 and 24.Alternatively, a single resistor which extends between the paths may beused or just one resistor may be employed to create enough heat to meltat least one solder joint connected to a spring as described below.

FIG. 2C illustrates a dielectric layer 35 disposed on substrate 15 whichcovers resistive elements 32 and 34. An opening 36 is formed throughdielectric layer 35 to provide a connection means to conducting path 22.Dielectric layer 35 may be, for example, glass having a desired thermalconductivity to allow the heat generated by the resistors 32, 34 to passtherethrough.

FIG. 2D illustrates a first conducting pad 42 disposed on dielectriclayer 35 above first resistive element 32 and a second conducting pad 44disposed on dielectric layer 35. First conducting pad 42 forms aconnection with first terminal 20 ₁ and second conducting pad 44 forms aconnection with second terminal 20 ₂.

FIG. 2E illustrates a dielectric layer 45 for example, glass, isdisposed partially over conducting pads 42, 44 and opening 36 resultingin exposed portions of the underlying conducting pads which becomesolder joint pads 46, 47 and 48. Low temperature melt solder is disposedon solder pads 46,47 and 48. Pad 48 is used to conduct current from aspring (shown in FIG. 2F) to a control circuit via terminal 20 ₃ duringan abnormal circuit condition as discussed below.

FIG. 2F illustrates a generally “V” shaped leaf-type spring 70 having apair of sides 70 ₁, 70 ₂ extending from an apex portion 71. Therespective ends 72, 74 of the sides 70 _(k), 70 ₂ are connected tosolder pads 46 and 47 via solder 46′, 47′ and the apex is soldered tosolder pad 48. Spring 70 may be made from, for example, high carbonsteel plated with silver, a shape memory alloy material, or similarconducting material and may, of course, have alternative geometriesattached to respective solder pads. A plastic cover is disposed over thecircuit protection device 10′ and glued about ledge 59 around theperimeter of substrate 12. FIG. 2G is a schematic view of the protectivedevice 10′ including resistive elements 32, 34, solder material 46′, 47′and first terminal 20 ₁, second terminal 20 ₂ and third terminal 20 ₃.

FIG. 2H is a side view of the protection device 10′ utilizing a leafspring 70 disposed on substrate 12 during normal current flow. Duringnormal operation, current flows as described above with reference toFIGS. 1H and 1I. However in this embodiment, when an over voltagesituation is detected at the load, a control circuit (not shown)connected to terminal 20 ₃ closes the circuit and draws current from thespring 70 via conducting path 22. This current flows through resistors32 and 34 which produces heat and melts one or more of the solderconnections 46′ and/or 47′, thereby releasing one or more of the springends 72, 74.

FIG. 21 is a side view of the protection device 10′ after the leafspring 70 is in an open position. The melting of one of more of thesolder joints snaps at least one side 70 ₁, and/or 70 ₂ of spring 70upwards which creates an open circuit thereby protecting the connectedbattery cells.

FIGS. 3A-3G illustrate a protection device 100 utilizing a spring inaccordance with an alternative embodiment having a plurality of layers.In particular, FIG. 1A is a plan view of a first layer defined bymetalized conducting paths 123 and 124 disposed on substrate 115. Afirst terminal 120 ₁, second terminal 120 ₂ and third terminal 120 ₃ areused to connect the protection device between a source of charge and apower source such as, for example, a plurality of battery cells. A firstresistive element 132 and second resistive element 134 are disposed onconducing paths 123 and 124.

FIG. 3B illustrates a dielectric layer 135 disposed on substrate 115which covers resistive elements 132 and 134. A opening 136 is formedthrough dielectric layer 135 to provide a connection means to conductingpath 124. Dielectric layer 135 may be, for example, glass having adesired thermal conductivity to allow the heat generated by theresistors 132, 134 to pass therethrough. FIG. 3C illustrates a plan viewof protective device 100 having a first conducting pad 142 disposed ondielectric layer 135 above first resistive element 132. A secondconducting pad 143 is disposed on dielectric layer 135 and forms aconnection with conducting path 124 through opening 136. A thirdconducting pad 144 is disposed on dielectric layer 135 above secondresistive element 134. As shown in FIG. 3D, solder material 152 isdisposed on first conducting pad 142 and solder material 154 is disposedon conducting pad 144. Both solders 152 and 154 may be a low temperaturemelt solder or one of solders 152 or 154 may be a low temperature meltsolder and the other solder may be a high temperature melt solder. Thelow temperature melt solder employed is configured to melt at a desiredtemperature consistent with the heat produced by resistive elements 132and 134 during an over-voltage or over-temperature condition.

FIG. 3E is a schematic view of protective device 100 including resistiveelements 132, 134, low melt solder material 152, 154 and first terminal120 ₁, second terminal 120 ₂ and third terminal 120 ₃.

FIG. 3F is a plan view of another of the various layers of theprotection device 100 disposed on substrate 115 including a spring 160electrically connected to conducting pad 143 via weld areas 161.Although spring 160 is illustrated having a substantially rectangularshape, alternative configurations may be employed. A first end 162 ofspring 160 is connected to conducting pad 142 via solder 152 and asecond end 164 of spring 160 is connected to conducting pad 144 viasolder 154. Spring 160 may be made from, for example, beryllium copper,high-carbon steel or other spring alloy. The spring may plated with amaterial such as silver or gold to increase its electrical conductivity.Alternatively, a low resistance shunt wire may extend of one end of thespring to the other to carry the majority of the current under normalbattery charge and discharge operation.

FIG. 3G is a side view of the various layers of protection device 100.In particular, spring 160 is connected to terminal 120 ₃ by way of via136 and conducting pad 143 a portion of which is disposed in via 136.Dielectric layer 135 is disposed between substrate 115 and conductingpads 142, 143 and 144. Spring 160 is disposed on conducting pad 143conducting pads 142 and 144 via solder 152 and 154 respectively. Duringnormal operation, current flows from terminal 120 ₁ through conductingpad 142 to first end 162 of spring 160 via solder 152, through spring160 to second end 164, to conducting pad 144 via solder 154 to terminal120 ₂ and onto the connected power source.

As shown in FIG. 3H, when an abnormal voltage or temperature situationis detected, a control circuit (not shown) connected to terminal 120 ₃closes the circuit and draws current from the spring 160 throughconducting pad 143 disposed underneath the middle section of the spring160 to conducting path 123 connected to terminal 120 ₃. Because thiscurrent flows through resistors 132 and 134, heat is produced whichmelts one or more of the low melt solder joints 152 and/or 154. Themelting of one of more of the solder joints 152 and/or 154 releases thespring at one or both ends 162, 164. The releasing of one or both ends162, 164 of spring 160 away from the conducting pads 142, 144 opens thecircuit thereby protecting the connected power source. In this manner,protection device 100 utilizes a spring disposed within a plurality oflayers that produces an open circuit when an undesirable electricalcondition occurs within a charging circuit.

FIGS. 4A-4G illustrate a protection device 200 having a plurality oflayers utilizing a diffusion layer to provide an open circuitconfiguration in accordance with an alternative embodiment. Inparticular, FIG. 4A is a plan view of a first layer defined by metalizedconducting paths 223 and 224 disposed on substrate 215. A first terminal220 ₁, second terminal 220 ₂ and third terminal 220 ₃ are used toconnect the protection device between a source of charge and a load suchas, for example, a plurality of battery cells. A first resistive element232 and second resistive element 234 are disposed on conducing paths 223and 224.

FIG. 4B illustrates a dielectric layer 235 disposed on substrate 215which covers resistive elements 232 and 234. A via 236 is formed throughdielectric layer 235 to provide a connection means to conducting path224. Dielectric layer 235 may be, for example, glass having a desiredthermal conductivity to allow the heat generated by the resistors 232,234 to pass therethrough. FIG. 4C illustrates a plan view of circuitprotection device 200 having a first conducting pad 242 disposed ondielectric layer 235 above first resistive element 232. A secondconducting pad 243 is disposed on dielectric layer 235 and forms aconnection with conducting path 224 through via 236. A third conductingpath 244 is disposed on dielectric layer 235 above second resistiveelement 234.

FIG. 4D is also a plan view of circuit protection device 200 wherein adiffusion layer 250 is disposed, at least partially, over the layer ofconducting pads 242, 243 and 244. Diffusion layer 250 is defined by afirst end 252 disposed over resistive element 232, a second end 254disposed over resistive element 234 and a middle section 253 disposedover conducting pad 243. Diffusion layer 250 may be, for example a thinfilm of gold. The diffusion layer material employed is configured todiffuse into layers 235 and/or 260 at a desired temperature from heatgenerated by resistive elements 232, 234 associated with an abnormalcircuit condition.

FIG. 4E is a schematic view of the diffusion layer circuit protectiondevice 200 including resistive elements 232, 234, first terminal 220 ₁,second terminal 220 ₂, third terminal 220 ₃ and diffusion layer endportions 252 and 254. During normal operation, current flows fromterminal 220 ₁ through conducting pad 242 to first end 262 of diffusionlayer 250, through layer 250 to second end 254, to conducting pad 244 toterminal 220 ₂ and onto the connected device.

FIG. 4F is a plan view of circuit protection device 200 having a glasscover layer 260 disposed over diffusion layer 250 on substrate 215. FIG.4G is a side view of the various layers of circuit protection device 200illustrating glass cover layer 260 disposed on substrate 215 andconducting pad 243 filling via 236. Glass layer 260 is configured toabsorb diffusion of layer 250 during an abnormal circuit condition. Inparticular, when an over-voltage or over-temperature situation isdetected, a control circuit (not shown) connected to terminal 220 ₃closes the circuit and draws current from diffusion layer 250 throughconducting pad 243 disposed underneath the middle section 253 ofdiffusion layer 250 to conducting path 223 connected to terminal 220 ₃.Because this current flows through resistive elements 232 and 234,enough heat is produced which causes the diffusion layer end portions252 and/or 254 disposed above resistive elements 232, 234 to diffuseinto layers 235 and or 260. One or more portions diffuse into glasslayer 235 and/or 260 which opens the circuit at one or both ends 252and/or 254 of diffusion layer 250. The diffusion of one or both ends252, 254 of layer 250 into glass layers 235 and/or 260 opens the circuitthereby protecting the connected device. In this manner, circuitprotection device 200 utilizes a diffusion layer disposed within aplurality of layers that produces an open circuit when an undesirableelectrical condition occurs within a charging circuit.

FIGS. 5A-5G illustrate a circuit protection device 300 having aplurality of layers utilizing a thermal link that, when opened, providesan open circuit configuration in accordance with an alternativeembodiment. In particular, FIG. 5A is a plan view of a first layerdefined by metalized conducting paths 323 and 324 disposed on substrate315. A first terminal 320 ₁, second terminal 320 ₂ and third terminal320 ₃ are used to connect the circuit protection device between a sourceof charge and a power source such as, for example, a plurality ofbattery cells. A first resistive element 332 and second resistiveelement 334 are disposed on conducting paths 323 and 324.

FIG. 5B illustrates a dielectric layer 335 disposed on substrate 315which covers resistive elements 332 and 334. A via 336 is formed throughdielectric layer 335 to provide a connection means to conducting path324. Dielectric layer 335 may be, for example, glass having a desiredthermal conductivity to allow the heat generated by the resistors 332,334 to pass therethrough. FIG. 5C illustrates a plan view of circuitprotective device 300 having a first conducting pad 342 disposed ondielectric layer 335 above first resistive element 332. A secondconducting pad 343 is disposed on dielectric layer 335 and forms aconnection with conducting path 324 through via 336. A third conductingpad 344 is disposed on dielectric layer 335 above second resistiveelement 334.

FIG. 5D is also a plan view of circuit protection device 300 wherein athermal link layer 350 is disposed, at least partially, over the layerof conducting paths 242, 243 and 244 and dielectric layer 335. Thermallink layer 350 is defined by a first end 352 disposed over resistiveelement 332, a second end 354 disposed over resistive element 334 and amiddle section 353 disposed over conducting pad 343. Thermal link layer350 is configured with a low temperature melting point at least at theportions of first end portion 352 and second end portion 354 disposedover respective resistive elements 332 and 334. The thermal link layeremployed is configured to melt at a desired temperature from heatgenerated by resistive elements 332, 334 associated with an over voltagecondition.

FIG. 5E is a schematic view of the thermal link layer circuit protectiondevice 300 including resistive elements 332, 334, first terminal 320 ₁,second terminal 320 ₂, third terminal 320 ₃ and thermal link portions352 and 354. During normal operation, current flows from terminal 320 ₁through conducting pad 342 to first end 362 of thermal link layer 350,through layer 350 to second end 354, to conducting pad 344 to terminal320 ₂ and onto the connected load.

FIG. 5F is a plan view of circuit protection device 300 having a hotmelt adhesive (HMA) cover layer 360 disposed over thermal link layer 350on substrate 315. FIG. 5G is a side view of the various layers ofcircuit protection device 300 illustrating the HMA layer 360 disposed onsubstrate 315 and conducting pad 343 filling via 336. HMA layer 360 isconfigured to absorb thermal link layer 360 during an over voltagecondition. In particular, when an abnormal circuit condition is detectedat the load, a control circuit (not shown) connected to terminal 320 ₃closes the circuit and draws current from thermal link layer 350 throughconducting pad 343 disposed underneath the middle section 353 of thermallink layer 350 to conducting path 323 connected to terminal 320 ₃.Because this current flows through resistive elements 332 and 334,enough heat is produced which melts one or more thermal link layer endportions 352 and/or 354 disposed above resistive elements 332, 334 whichdisperse into HMA cover layer 360. The one or more melted thermal linklayer portions melt into HMA cover layer 360 which opens the circuit atone or both ends 352 and/or 354 of thermal link layer 350, therebyprotecting the connected load. In this manner, circuit protection device300 utilizes a thermal link layer disposed within a plurality of layersthat produces an open circuit when an undesirable electrical conditionoccurs within a charging circuit.

FIG. 6 illustrates an exemplary embodiment of a cover 600 described withreference to FIGS. 1-5 and denoted in FIG. 5G as cover 360. Cover 600 isdisposed over each of the circuit protection devices 10, 10′, 100, 200and 300 adhered around the perimeter of the respective substrates 15,115, 215, and 315. Typically, cover 600 is bonded to the respectivedevice using an epoxy, but alternative adhesives may be used. Cover 600includes portions 601 which provide added surface areas around the cover600 to allow for improved bond strength with the epoxy. In addition,portions 601 may have a roughened or textured surface to further improvebond strength with the epoxy. Through holes 602 a . . . 602 d may bedisposed proximate respective portions 601. These holes may be taperedand used to receive epoxy or other adhesive and act as a “locking”feature for cover 600 on the respective substrates. In addition, thethrough holes 602 a-602 d may also be disposed at various locations oncover 600. By way of example, by using the combination of portions 601and through holes 602, cover 600 is able to withstand a pull force up toabout 5.8 lbs as compared to a typical industry standard of about 1.12lbs.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

1.-19. (canceled)
 20. A circuit protection device comprising: asubstrate; a conducting layer disposed on said substrate, saidconducting layer having at least a first and second terminals; aresistive element disposed at least partially on said conducting layer;a conducting pad disposed over said resistive element; a diffusion layerdisposed over said conducting pad; and a glass layer disposed over thediffusion layer wherein when an abnormal circuit condition occurs heatis generated by the resistive element which causes a portion of thediffusion layer to diffuse into the glass layer to create an opencircuit between the first and second terminals.
 21. The circuitprotection device of claim 20 further comprising a dielectric layerdisposed over said resistive element, said dielectric layer having a viatherethrough to electrically connect at least a portion of saidconducting pad with said conducting layer.
 22. A circuit protectiondevice comprising: a substrate; a conducting layer disposed on saidsubstrate, said conducting layer having at least a first and secondterminals; a resistive element disposed at least partially on saidconducting layer; a conducting pad disposed over said resistive element;a thermal link layer disposed over said conducting pad; and a hot meltadhesive (HMA) cover layer disposed over the thermal link layer whereinwhen an abnormal circuit condition occurs heat is generated by theresistive element which causes a portion of the HMA layer to absorb thethermal link layer to create an open circuit between the first andsecond terminals.
 23. The circuit protection device of claim 22 furthercomprising a dielectric layer disposed over said resistive element, saiddielectric layer having a via therethrough to electrically connect atleast a portion of said conducting pad with said conducting layer. 24.The circuit protection device of claim 20, wherein the resistive elementis a first resistive element, the device further comprising a secondresistive element disposed at least partially on said conducting layer.25. The circuit protection device of claim 21, wherein the dielectriclayer is glass having a desired thermal conductivity such that heatgenerated by the resistive element passes therethrough.
 26. The circuitprotection device of claim 20, wherein the diffusion layer is a thinfilm metallic layer.
 27. The circuit protection device of claim 20,wherein said conducting layer comprises a third terminal, the devicefurther comprising a control circuit connected to the third terminal,the control circuit configured to draw current from the diffusion layerduring the abnormal circuit condition.
 28. The circuit protection deviceof claim 22, wherein the resistive element is a first resistive element,the device further comprising a second resistive element disposed atleast partially on said conducting layer.
 29. The circuit protectiondevice of claim 23, wherein the dielectric layer is glass having adesired thermal conductivity such that heat generated by the resistiveelement passes therethrough.
 30. The circuit protection device of claim22, wherein the thermal link layer is a configured to melt at a desiredtemperature from heat generated by the resistive element.
 31. Thecircuit protection device of claim 22, wherein said conducting layercomprises a third terminal, the device further comprising a controlcircuit connected to the third terminal, the control circuit configuredto draw current from the diffusion layer during the abnormal circuitcondition.